1. Field of the Invention
The present invention relates generally to dry etching methods of interconnection layers and more particularly to a dry etching method for interconnection layers which is improved so that a sufficient etching rate can be obtained without heating substrates to high temperature.
2. Description of the Background Art
With development of higher integration, higher performance and higher speed of semiconductor devices, metal film interconnections in semiconductor devices (LSI, for example) are increasingly miniaturized. With miniaturization of the metal film interconnection, the density of current flowing in the metal film interconnection is on a steady increase recently. As a result, for the reliability demanded for the metal film interconnection, that is, electromigration resistance and stress migration resistance, extremely high characteristics are demanded. Accordingly, materials of the metal film interconnection are also under development.
For example, describing a dynamic random access memory (DRAM), before units of 156Kbit were developed, aluminum-silicon alloy (AlSi) has been employed for the metal film interconnection. In the generation of 1 Mbit-16 Mbit, in order to enhance the electromigration resistance and the stress migration resistance, AlSiCu alloy to which copper is added is employed for the metal film interconnection. Under such conditions, in the generation of 64 Mbit or larger, because of demand for further improvement in the reliability, it is almost sure that interconnection employing copper or copper alloy will be employed.
Accordingly, for manufacturing DRAMs of 64 Mbit or larger, development in the fine processing technology of Cu and Cu alloy films is essential.
However, the fine processing technology of Cu and Cu alloy films, that is, the dry etching technology has not been satisfactory. Although a copper dry etching method employing methyl iodide has been proposed, as one relating to the present invention (Japanese Patent Laying-Open No. 60-86285), it is not satisfactory as will be described later referring table 1.
FIG. 4 is a partial sectional view of a semiconductor device in order of respective steps in a conventional dry etching method for Cu or Cu alloy films. FIG. 5 is a schematic diagram of a reactive ion etching device for implementing the dry etching. Before describing the conventional dry etching method shown in FIG. 4, the structure of the reactive ion etching apparatus shown in FIG. 5 will be described first.
Referring to FIG. 5, the reactive ion etching device includes a hollow processing container 1. In the processing container 1, an upper plate high frequency electrode 2 and a lower plate high frequency electrode 3 arranged parallel to each other are provided. An exhaust port 6 for exhausting gas in processing container 1 to implement a vacuum condition inside processing container 1 is provided at a lower portion of processing container 1. A gas introducing port 5 is provided at an upper portion of processing container 1 for introducing reactive gas containing chlorine type gas as a main component into processing container 1. An output on one side of a high frequency power source 7 is directly connected to the upper plate high frequency electrode 2. The other side output of high frequency power source 7 is connected to the lower plate high frequency electrode 3 through a capacitor 8 for high frequency coupling.
Next, referring to FIGS. 4 and 5, a conventional dry etching method for Cu or Cu alloy films will be described.
Referring to FIG. 4(a), a substrate to be processed 4 (hereinafter, referred to as a substrate 4) is prepared. The substrate 4 includes a silicon substrate 11, a silicon oxide film 12 (interlayer insulating film) provided on silicon substrate 11, an interconnection layer 13 formed of a Cu or Cu alloy film provided on silicon oxide film 12, and a resist pattern 14 provided on interconnection layer 13, for example.
Referring to FIG. 5, substrate 4 is carried on lower plate high frequency electrode 3. Next, a chlorine type reactive gas (e.g., HCl) is introduced into processing container 1 from gas introducing port 5 and simultaneously the gas is exhausted from exhausting port 6 to maintain predetermined pressure in processing container 1. A heater 9 is operated to keep lower plate high frequency electrode 3 and substrate 4 at predetermined temperature of 200.degree. C. or higher. The condition of substrate 4 at that time is shown in FIG. 4(b).
High frequency voltage coming from high frequency power source 7 is applied between lower plate high frequency electrode 3 and upper plate high frequency electrode 2 to produce plasma 10 of the reactive gas in processing container 1.
When plasma 10 is produced in processing container 1, lower plate high frequency electrode 3 is charged of negative potential and reactive ions produced in plasma 10 are accelerated by the potential to impinge upon substrate 4. Neutral radical molecules produced in plasma 10 also diffuse in the plasma to reach the substrate 4 surface. The chlorine type reactive ions and neutral radical reached the surface of substrate 4 react with Cu or Cu alloy at a portion not covered with resist pattern 14 to give reaction product mainly containing CuCl.sub.x, referring to FIG. 4(b). Substrate 4 is heated to temperature of 200.degree. C. or higher and the temperature of the surface of substrate 4 is as high as several hundreds .degree.C., the reaction product containing CuCl.sub.x as main component is evaporated to be removed from the surface of substrate 4. The etching of interconnection layer 13 using resist 14 as a mask thus proceeds.
Referring to FIGS. 4(b) and (c), removing resist pattern 14, interconnection pattern 13a of the Cu or Cu alloy is formed.
The conventional dry etching of Cu or Cu alloy has been performed employing plasma of chlorine type gas as described above. Accordingly, the vapor pressure of the obtained reaction product (CuCl.sub.x) is low, and substrate 4 had to be heated to 200.degree. C. or higher for obtaining a practical etching rate.
However, when substrate to be processed 4 is heated to 200.degree. C. or higher, as shown in FIG. 4(b), there has been a problem that the resist pattern 14 is melted and thus deformed due to the heat. When resist pattern 14 changes in its shape as shown in the figure, referring to FIG. 4(c), the sectional shape of interconnection pattern 13a is taper-shaped in the upward direction, which has been a problem in view of accuracy. Also, there has been a problem that the removal of resist pattern 14 after finishing etching becomes impossible.
As a method of solving the problem of deformation of resist pattern 14 by heat, the method of etching a Cu or Cu alloy employing a silicon oxide film as a mask shown in FIG. 6 is known.
That is, referring to FIG. 6(a), an interlayer insulating film 12 and a Cu or Cu alloy interconnection layer 13 are formed on a silicon substrate 11. A pattern 15 of a silicon oxide film is formed on Cu or Cu alloy interconnection layer 13.
Referring to FIG. 6(b), while heating silicon substrate 11 to the temperature of 200.degree. C. or higher, using pattern 15 of the silicon oxide film as a mask, Cu or Cu alloy interconnection layer 13 is patterned with plasma of chlorine type gas. By this method, the heat resistance of pattern 15 of the silicon oxide film is good, so that pattern 15 is not changed in its shape even if the substrate is heated to 200.degree. C. or higher. Accordingly, an interconnection pattern of the Cu or Cu alloy with high accuracy in which the side wall is perpendicular to the substrate can be obtained.
However, the method requires a step of forming pattern 15 of a silicon oxide film, resulting in problems of an increase in the number of manufacturing steps and an increase in manufacturing cost accordingly.